Conventionally, although there are diagnosing devices for precisely measuring a bone density as devices for diagnosing a bone strength using X-rays, they have a problem that the devices are large-scaled and one may be irradiated.
For this reason, devices utilizing an ultrasonic wave are used as noninvasive bone strength diagnosing devices which do not cause such a problem (for example, refer to JP2005-510283(A)). With such a diagnosing device, an ultrasonic wave is radiated from a wave-transmission device of the ultrasonic wave in a direction inclined by a predetermined angle with respect to a front surface of the bone to generate a surface wave on the front surface of the bone. Then, for example, a leaky wave leaking from the surface wave is received by a wave-reception device of the ultrasonic wave which is movable relative to the wave-transmission device of the ultrasonic wave, and after that, a speed of sound of the surface wave is measured based on a propagation time and a propagation distance from the radiation of the ultrasonic wave to the reception of the leaky wave. Such a device measures a long bone, such as a radius, a tibia, and a phalange, and therefore, it measures a speed of sound of the surface wave transmitted in the long bone along the longitudinal direction. Generally, the bone strength is diagnosed to be higher as the speed of sound of the measured surface wave becomes faster.